In recent years, a power storage battery is going large, studied so as to be used to store power that is consumed in households, stores, buildings and the like. This power storage battery is able to perform a discharge (supply power) at any timing by being charged (consumes power) beforehand. In other words, by controlling the timing for performing the charge and discharge of the power storage battery, it becomes possible to control a timing when system power (power supplied form an electric power company) is consumed.
Generally, the power rate of system power includes a fixed basic rate and a measured use rate. And, an electric power company sets the power rate such that the basic rate becomes more inexpensive as the maximum value of system power amount consumed during a unit time becomes smaller. Besides, the power rate is set such that the use price per unit power becomes more inexpensive during a night when the power consumption is likely to become small than during a daytime when the power consumption is likely to become large. Because of this, a user of the system power can reduce payment of the power rate more as the power consumption is more leveled. And, if the power consumption is leveled, an electric company becomes able to efficiently perform the power generation (especially, thermal power generation), accordingly, it becomes possible to reduce the amount of carbon dioxide emission due to the power generation.
The leveling of the power consumption is achievable by, for example, discharging a power storage battery in a case where the power amount consumed per unit time becomes large instantaneously, or by charging the power storage battery during a night and discharging the power storage battery during a daytime. In the case of controlling such a charge and a discharge of the power storage battery, if a residual amount of the power storage battery is exactly measured to decide the timing for performing the charge and discharge and the power amount to be charged and discharged, it is possible to effectively achieve the leveling of the power consumption, which is accordingly preferable.
As methods for measuring the residual amount of the power storage battery, there are, for example: a method that estimates the residual amount based on a voltage value of the power storage battery; and a method that uses a state (e.g., a sufficiently charged state) as a reference and estimates the residual amount by integrating an amount of charged and discharged electric current. However, according to these methods, the estimation accuracy deteriorates because of use of the power storage battery and time passage, it becomes impossible to obtain the exact residual amount, which becomes a problem.
As a method for solving the problem, there is a method for performing a full charge and a full discharge of the power storage battery and obtaining again the residual amount of the power storage battery by means of actual measurement (hereinafter, called amount learning). By obtaining periodically the amount of the power storage battery by means of the amount learning and reflecting the obtained amount of the power storage battery into the estimation method of the residual amount of the power storage battery, it becomes possible to obtain the residual amount of the power storage battery with high accuracy.
For example, a patent document 1 proposes an amount learning method in which if a command for performing the amount learning is issued by a user, the power consumption by a system including the power storage battery is maximized, whereby the full discharge of the power storage battery is quickly performed.